Conventionally, a gas sensor detects gas from variation of current arising from contact of a sensitive film, for which, for example, tin dioxide or the like is used, and gas with each other.
In such a gas sensor as just described, since current is supplied using a constant current power supply, power consumption is high. Further, since the gas sensor is heated to a temperature at which a good detection characteristic is obtained, much power is consumed by a heater for heating the gas sensor.
Thus, also a gas sensor is available which detects gas based on a potential difference arising from absorption of gas. For example, in such a gas sensor as just described, an electrode having reactivity with respect to detection target gas and an electrode that is inactive to the detection target gas are provided on the opposite faces of a solid electrolyte layer such that gas is detected based on a potential difference generated as a result of chemical reaction occurring by the contact with gas.